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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

PITCH

321

PITCH

This exists in the three forms, soft, hard and extra hard, and the tests
made are for the purpose of ascertaining to which class the sample belongs
and hence to what uses it may well be put.

1 Determination of the Specific Gravity.—With the picnometer
in the ordinary way for solids ; very hard pitches should first be powdered.

2.  Determination of the Free Carbon.—As with tar (see Crude Tar,
3, P- 3i8).

3.  Determination of the Ash.—2 or 3 grams of the pitch are burnt
in a porcelain crucible in a muffle and the residue weighed.

4.  Determination of the Volatile Matter and Coke.—As with fuels
(g.v.).    It is important to note the appearance of the coke—whether swollen,
compact or coked.

5.  Softening and Melting Temperatures.—These serve better than
other tests to indicate the degree of purity of the pitch.    In a beaker of
water containing about half a litre of water is suspended a cube of the pitch
of about 13 mm. side or a disc 4-5 mm. thick at the end of an iron wire,
the pitch being 5 cm. from the bottom.   A thermometer is immersed with
the bulb at the same depth as the pitch and the temperature of the water
raised 5° per minute.    From time to time the pitch is withdrawn to ascertain
how it behaves when pressed between the fingers.   The temperature of
incipient softening is taken as the lowest at which the pitch can be twisted
without breaking, while the temperature of softening is that at which it can
be moulded between the fingers without force and the melting point as that
at which it begins to drop.

6.  Distinction between  Tar  Pitch,  other Pitches  and  Natural
Asphalt.—The characters of these products are as follows:

Coal-tar Pitch.
	Vegetable Pitch (Black or Marine Pitch).
	Petroleum Pitch.
	Stearine Pitch.
	Natural Bitumen.

Black, more
	Black,   with   an
	Black, almost
	Black, odour
	BlacMsh, usu-

or less stiff,
	odour   recalling
	odourless.
	of fatty sub-
	ally   solid

with an odour
	that    of   vege-
	
	stances.
	and   hard,

of tar.
	table tar.
	
	
	sometimes


	
	
	
	soft.

Slightly soluble
	Very   soluble   in
	Almost com-
	Insoluble    in
	Insoluble     in

in     alcohol,
	alcohol, giving a
	pletely    in-
	alcohol and
	alcohol;

the solution
	brown   solution
	soluble     in
	part ia lly
	does not give

giving    the
	containing resin-
	petroleum
	soluble     in
	the reactions

reactions
	ous matters and
	ether.
	petroleum
	for phenols.

for phenols ;
	giving   the   re-
	
	ether.
	

very slightly
	actions for phen-
	
	
	

soluble      in
	ols.    It  colours
	
	
	

light   petro-
	potash  solution
	
	
	

leum.
	brown.
	
	
	

The   distillate
	The distillate has
	In general has
	Has a saponi-
	

has an alka-
	an acid reaction.
	no saponifi-
	fication num-
	

line reaction.
	
	cation num-
	ber and  an
	


	
	ber.
	acid number.
	


	
	
	Evolves acro-
	


	
	
	lein      when
	


	
	
	heated.
	

A.C.

21tillation use is made of a condenser, which is removed